Key checkpoints in the movement of plant viruses through the host

Defenses against Virus and Vector: A Phloem-Biological Perspective on RTM- and SLI1-Mediated Resistance to Potyviruses and Aphids

“…One of the unresolved issues of phloem mobility is whether viral molecules require certain motifs or chaperones to hitchhike and move along with the phloem sap flow. The broad range of phloem-mobile mRNAs suggests that there may not be any required phloem-specific motifs for long-distance transport of host nucleotides [78]. There is, however, evidence that viruses are chaperoned by phloem-mobile host proteins [79][80][81].…”

Small hydrophobic viral proteins involved in intercellular movement of diverse plant virus genomes

“…Thus, modification of PD SEL by plant viruses is absolutely required for their movement from cell to cell. To perform their intercellular transport via Pd, viruses have evolved to encode specialized transport systems that usurp pre-existing host pathways for symplastic macromolecular communication in plants [12] – [18] . Retrospectively, over 40 years have passed since the hypotheses were put forward that consider the virus movement in plants as an active process used by plant viruses (particularly, tobacco mosaic virus) to spread both locally and systemically throughout plant bodies with the aid of specialized movement proteins (MPs, or transport proteins-TPs) [19] – [22] .…”

“…Some MPs in single MP-encoding viruses, similar to the TMV 30-kDa protein, possess all required protein domains (motifs) to perform cell-to-cell movement independently from other virus-specific proteins. Moreover, such single MP-encoding viruses are generally capable of sequence non-specific RNA binding and can assist the movement of other transport-deficient viruses [9] , [12] , [18] , [27] – [29] .…”

“…However, there is a special protein class of ‘30-kDa’-like MPs [30] , which use an alternative mechanism for cell-to-cell transport. This mechanism includes the displacement of the Pd internal structures including the desmotubule by a tubular structure formed by viral MP and the transfer of whole virions inside the tubule from infected cells to neighboring cells [9] , [12] , [18] , [31] . Virions can pass Pd inside MP-formed tubule in some positive strand RNA viruses, namely, comoviruses and nepoviruses (family Secoviridae ) [31] , [32] , and pararetroviruses [18] , [33] – [37] .…”

“…This mechanism includes the displacement of the Pd internal structures including the desmotubule by a tubular structure formed by viral MP and the transfer of whole virions inside the tubule from infected cells to neighboring cells [9] , [12] , [18] , [31] . Virions can pass Pd inside MP-formed tubule in some positive strand RNA viruses, namely, comoviruses and nepoviruses (family Secoviridae ) [31] , [32] , and pararetroviruses [18] , [33] – [37] . Analogously, plant negative strand RNA viruses representing families Tospoviridae and Aspiviridae encode ‘30-kDa’-like MP performing tubule-guided cell-to-cell movement of capsid RNPs [38] – [41] .…”